Chitin, chitosan and quaternary chitosan films were prepared, and the mechanical properties and the antibacterial activities of chitosan and quaternary chitosan films were evaluated. The tensile strength of chitin films was 30-40% lower than that of chitosan films, but the crystallinity of the former was much higher than those of the latter. A detailed analysis of the crystallinity and orientation of crystallites of chitosan films revealed that the cast film prepared with acetic acid provided a little lower crystallinity than the others. The antibacterial activities of quaternary chitosan films against Staphylococcus aureus and Escherichia coil were stronger than those of chitosan films. The antibacterial activities of neutralized chitosan films may be slightly inferior to those of un-neutralized chitosan films. The improvement in the antibacterial activity of chitosan films against E. coli was slightly inferior to that against S. aureus. This phenomenon was particularly observed on the neutralized chitosan films. Though the antibacterial activity of chitosan was slightly inferior to that of the organic antibacterial compounds, we emphasize that chitosan would be a useful and suitable material with regard to its effect on the environmental ecosystem.